Within the food industry, beverages and other products are often packed in paper or paperboard based packages. Packages intended for liquid food are often produced from a packaging laminate comprising a core layer of paper or paperboard and an outer, liquid-tight layer of thermoplastic material on at least that side of the core layer which will form the inside of the packages.
One kind of frequently occurring packages are the so-called carton bottles. In substance, these are composed of a lower part in the form of a sleeve of packaging laminate like the one described above, and an upper part in the form of a plastic top having a neck which is provided with an opening/closing means, such as a screw cap.
The carton bottles are often produced in that sheets, so-called blanks, of packaging laminate are formed into tubes which are closed by sealing of two opposing edges of each sheet in an overlapping condition. Then, according to a first variant, a top of thermoplastic material is directly injection-moulded onto the tube at one end. The injection-moulded top could have a neck sealed by a membrane for subsequent provision of a screw cap. Alternatively, the top could be injection moulded using the screw cap as a part of the moulding cast. In such a case, the package is provided with the screw cap in connection with the injection moulding of the top. After injection-moulding, the package is filled, sealed at the open end of the tube for achieving a sleeve and closing the package, and formed into the desired shape.
According to a second variant, instead of injection-moulding a top directly onto the tube, the tube is slipped over a respective premade plastic top and arranged in such a way that a major part of the top protrudes from the tube. The premade top has a neck closed by a screw cap. After sealing of the top and the tube along a contact surface between them, the package is filled, sealed at the open end of the tube for achieving a sleeve and closing the package, and finally formed into the desired shape.
The above manufacturing methods are well-known in the art and will not be described in greater detail.
In order to extend the shelf-life of the packed product, it is known in the art to sterilize the packages before the filling operation. Depending upon the desired length of shelf-life, and depending upon whether the packages are to be distributed and stored in a refrigerated environment or at room temperature, different levels of sterilization may be selected.
As an example, chemical sterilization can be used for sterilizing open carton bottles before filling. One sterilization apparatus for gas phase sterilization of carton bottles is described in published international application WO2004/054883, which is hereby incorporated herein by reference. The patent specification discloses how the carton bottles are sterilized in that, disposed upside down on a conveyor belt, they are caused to pass first through a heating zone, then a sterilization zone and finally a venting zone. In the sterilization zone, the carton bottles are subjected to gaseous hydrogen peroxide. In order to prevent the hydrogen peroxide from condensing on the surface of the carton bottles in the sterilization zone, which impedes later removal, the carton bottles are heated up in the heating zone to a temperature above the dew point of the hydrogen peroxide gas. In the venting zone, the carton bottles are subjected to sterile hot air in order to vent off hydrogen peroxide which remains in and on the carton bottles. After sterilization, the interior of the carton bottles needs to be kept under aseptic conditions until filling with product and subsequently sealing.
To be able to achieve a satisfactory sterilization of the carton bottles, the conditions of the respective zones must be maintained. To this end, as described more closely in WO2004/054883, the zones are separated from each other by partitionings. Further, a higher pressure is maintained in the sterilization zone than in the heating and venting zones to prevent flows from the heating and venting zones into the sterilization zone.
In order to obtain a satisfactory sterilization of the carton bottles, they must be subjected to a sufficiently high sterilizing gas concentration for a sufficiently long time, i.e. a stable, sufficiently high hydrogen peroxide concentration should be maintained throughout the sterilization zone. Further, to maintain the positive pressure inside the sterilization zone, a very strong inflow into the sterilization zone is required because of the significant outflow through the partitionings separating the sterilization zone from the heating and venting zones, respectively. This will result in large emissions of gaseous hydrogen peroxide form the sterilization zone, which emissions require appropriate handling. Naturally, this will also result in a large consumption of hydrogen peroxide.